This invention relates to an adaptive pulsing system for controlling a motor which moves a device to a desired position. The invention is useful wherever it is desired to have precise position control, i.e., very accurately determined movement to destination.
In abandoned Sweeney appliction Ser. No. 289,922, filed Aug. 4, 1981, and assigned to the assignee of this application, a positioning system is disclosed utilizing a synchronous pulsing system which varies the energy exerted during a predetermined "on" period. In other words, the motor "on" portion of each cycle is a predetermined "window", or period, of time; and the motor "off" portion of each cycle is also a predetermined period of time, the two periods having a ratio which depends on the type of machine being operated. Within the "on" window, a "nudging" technique is used during final approach to move the driven element by providing initially a lesser amount of energy during the period of one "on" window, and gradually increasing the amount of energy during each successive "on" window, until forward movement is detected. Then the cycle begins again with the lesser amount of energy. Thus, the duration of the actuation period ("on" window) is constant, but the driving energy is varied within the "on" window. This variation preferably is accomplished by varying the duty cycle of the motor. And the preferred way of causing the duty cycle variation is to provide motor driving pulses whose width is varied to alter the ratio of "on" and "off" time within the "on" window.
In both Ser. No. 289,922 and its predecessor application, Sweeney application Ser. No. 173,274, which is now U.S. Pat. No. 4,353,019, and which is also assigned to the assignee of this application, the final, or terminal, approach to the destination is accomplished by the aforementioned "nudging" technique, in which pulses providing successively increasing amounts of motor-driving energy are used until forward motion of the driven element is detected, at which time the driving pulse cycle starts again at the lowest value. This concept of a repetitive pulse-increasing cycle as the terminal pulsing approach, which would seem to be contra-indicated by prior art teachings, has in fact demonstrated the ability to accomplish previously unattainable position accuracy.
In an earlier application of Sweeney et al, now U.S. Pat. No. 4,312,033, a destination-finding "proportional" technique is disclosed in which each interim target in a series of targets is set as a fraction of the remaining distance to destination. While the techniques disclosed in the later-filed applications have proved successful in attaining improved resolution, the system of U.S. Pat. No. 4,312,033 is still useful as a stage in the motion of the driven element just prior to the final "nudging" stage. Also, it is clearly useful to have an initial, fast motion stage which brings the driven elements to the vicinity of the destination, before the "proportional" and "nudging" stages are initiated.
It has now been perceived that a lack of optimization in all of the earlier approach systems has resulted from the preoccupation with avoiding destination overshoot at all costs. In other words, unnecessarily complicated systems, and systems which move more slowly than necessary, have resulted from an over-concern with the overshoot possibility. The present system is designed to convert the overshoot potential from a negative to a positive factor in the destination-finding system.
The present invention is concerned primarily with the automatic adjustment or "revaluation" of the quantitative values used in destination-finding systems similar to those of the applications identified above, i.e., such initial values as the duty cycle which begins each series of duty cycle changes, and the position to which the system is driven in its initial rapid motion phase. In the systems of the previous applications, it was necessary to pre-select those values; and the initial values were set low enough to avoid overshoot. If the values were set too high, overshoot would be unavoidable, and repetitive. If, to counteract that possibility, the initial values were set very low, then an unnecessarily complicated and slow approach to destination would result.
The operating characteristics of positioning machines, i.e. the energy required to move them, will differ because of several variables, such as their mechanical characteristics, the loads they encounter in different situations, and the quality of their maintenance. Also different axes of the same machine may have different operating characteristics. As stated above, in prior machines of the type discussed herein, it has been necessary to set low initial values of target position and/or driving energy because, otherwise, the machine would tend to overshoot frequently, and therefore be unreliable.